JP6738897B2 - Optimized drawing and wall ironing method for aluminum containers - Google Patents

Description

The present invention is produced by squeezing and ironing, i.e. according to a method which specifically comprises these two basic steps, to those skilled in the art as "cans" or "beverage cans" or even "two-piece beer cans and beverages". It relates to the field of aluminum alloy beverage cans or containers, also known as "cans".

The present invention is more particularly optimized for this type of application, which has the particular advantage of providing lower tear rates, better can geometry consistency, and better can surface morphology. Regarding ironing method.

This improvement includes controlled roughness and texture of the punch, ironing die geometry (land width, work area roughness, inlet geometry), and aluminum sheet (metal internal and external roughness), and Obtained through copper lubrication.

Unless otherwise specified, aluminum alloys are referred to below according to the names defined by the "Aluminum Institute" in its "Registration Record Series" which are published regularly.

Unless specified otherwise, the metallurgical tempering definitions listed in European Standard EN 515 apply. The static tensile mechanical properties, in other words the maximum tensile strength Rm (or UTS), the tensile yield force R _p0.2 (or YTS) and the elongation A% (or E%) at a plastic elongation of 0.2% are NF EN ISO. 6892-1 determined by a tensile test.

Aluminum alloys, due to their very attractive visual appearance, their suitability for recycling, and their high corrosion resistance, in particular compared to plastics or steel, make containers, and more particularly beverage cans. Is increasingly used in the manufacture of.

Beverage cans, also known to those of ordinary skill in the art as "cans" or "two-piece beverage cans", typically employ a 3104 type alloy sheet in a H19 metallurgical temper of 0.2-0.3 mm. Manufactured by drawing and ironing using a gauge.

The sheet undergoes a first operation for cupping, which consists of punching and drawing. More specifically, during this step, a sheet coil is replenished to a press, also known as a "copper," which press cuts a disk known as a blank and performs a first deep drawing operation. To produce "cups".

The cup is then transported to a second press, or "can bodymaker", where it undergoes at least one second deep drawing operation and multiple successive ironing operations. These operations consist of thinning and elongating the metal through a deep-drawn blank into an ironing tool known as a ring or die.

The bottom of the can is also shaped at this point. Malleable metal is formed into a cylindrical container without a lid. The sidewall of the can is significantly thinner than the bottom (dome), which is not ironed and remains close to the original starting gauge. The sidewalls of the can are constructed of what are commonly known as the middle wall and the top wall (see Figure 1).

The can is then trimmed to the desired height in a rotary machine.

During the ironing process, tearing (sidewall breaks or failures during the ironing process) can occur, causing a down of the can making machine that reduces line capacity. Moreover, after ironing, the can's glossy appearance can vary significantly.

According to Avittur (1983), "The force of the punch [...] Is transmitted partly to the [...] Deformation zone through the pressure on the bottom of the cup, and also by the tension on the wall and partly. As the friction between the punch and the inner surface of the cup increases, the tension exerted on the wall decreases, thus allowing ironing with greater reduction. With greater ram friction than die friction) and proper choice of die angle, in principle an infinite amount of reduction can be achieved through a single die... in practice until recently 1 It is known that the reduction obtained in a single drawing through two dies was only small..." (see Figure 2).

GB-A-1400801 (Avittur) uses a punch with a larger friction surface in the punch than in the die so that the tensile stress in the ironed zone is reduced or eliminated. A deep drawing process is disclosed in which a hollow workpiece is wall ironed through a conical die.

Japanese Laid-Open Patent Publication No. 57-7334 (Aki Kishimoto) discloses a prescribed shape and depth of a circumferential groove line designed to improve can ejection and formability in ironing of a can body. And a punch having a spacing is disclosed. The punch texture is not isotropic.

In JP-A-2007-275947 (Daiwa Seikan Co., Ltd.), the outer circumferential surface is divided into two parts so that the tip side part is rough and the base end side part is smooth. , A punch for ironing is disclosed.

Japanese Patent Laid-Open No. 61-212428 (Nippon Steel Corporation) discloses a steel sheet having improved ironing and stripping workability, which has different roughened surfaces on the front and back sides, respectively. doing.

U.S. Pat. No. 5,250,634 (Aluminum Company of America) discloses a metal sheet for making a hard container product having a crack-free surface that retains only trace amounts of lubricant.

Furthermore, according to the state of the art, the interaction between metal and tool, ie punch and metal and die and metal, is controlled using the following specifications:
The metal roughness Ra is 0.3 to 0.5 μm on both sides.
-Kopper lubrication is composed of two components: a post lubricant and a copper lubricant. Post lubricant, an aluminum manufacturer is applied for both sides at the level of the average 500 mg / m ^2, kappa lubricant is applied in the cupping press at a level of 500~1100mg / m ² for both sides. Thus, the total amount of lubricant (post-lubricant plus copper lubricant) is 1000-1600 mg/m ² , more specifically 16-24 mg per cup for a 33 cl can. To do. The distribution of the lubricant between both surfaces of the metal sheet is 50 to 60% on the outer side and 40 to 50% on the inner side.
The can-making machine punch has the surface polished and ground, ie the nose radius and the reworked Taber are ground (Ra≦0.05 μm) and the main body is ground (Ra≦0.3 μm). Delivered.
The can body making punch is textured by the can manufacturer using a process commonly known in the industry as cross-hatching. This process is different for each canmaker and can sometimes be poorly controlled.
The working surface of the ironing die has a feed angle (1), a land width (2) and its angle (3), an intersection (5) between the feed surface (7) and the land, an exit angle (4) and It is defined by the surface roughness of these areas (see Figure 3). Typically, the industry uses landing angles of 7-8° and land widths of 0.38-0.76 mm. The land angle (3) can be 0-5', thus becoming larger in diameter towards the exit of the land. The intersections (5) and (6) are sharpened between the infeed surface (7) and the land (8) and between the land and the exit surface (9), respectively. The exit angle (4) is between 2° and 8° and the surface roughness is typically defined as Ra≦0.05 μm or Ra≦0.10 μm. Currently, the average tear rate is 20 ppm to 150 ppm obtained using a standard three-time ironing die process with an effective ironing ratio of the third die of 38% to 44%. The standard 60° reflectance of the can is less than 73%. Typical top wall thickness variability is around 11 μm.

Because of the huge volume of beverage cans produced each year (320 billion), each slight improvement in the manufacturing process can result in significant savings.

British Patent Publication No. 1400081 JP 57-7334 A JP 2007-275947 A JP 61-212428 A US Pat. No. 5,250,634

The problem to be solved is to identify the best ironing conditions that guarantee a high production productivity such as a low tear rate or a low necking damage rate in a stable manner over a long period of time.

The glossy appearance of the outer wall of the can preform after ironing is an important property for the quality of the visual appearance of the final can product after decorating. The problem to be solved is to identify the highest ironing conditions that maximize the reflectance measured at 60° while keeping the manufacturing productivity mentioned above at a reasonable level. Finally, one of the main objectives is to reduce the amount of metal that is put into the can. It is believed that this can be done by reducing the thickness of the top wall, middle wall or dome. The problem to be solved is to identify the best ironing conditions that allow these thicknesses to be reduced by all means while keeping the production productivity mentioned above at a reasonable level.

The present invention, in the aluminum alloy beverage can manufacturing method by "drawing/ironing", higher than between the ironing die and the aluminum sheet, the friction between the can body manufacturing machine punch and the aluminum sheet,
An aluminum alloy sheet having an inner surface (typically Ra>0.4 μm for Ra<0.3 μm) with a significantly higher roughness than the outer surface,
An ironing die with rounded intersections between the feed and exit surfaces and the lands, the surface Ra in the working area being less than about 0.03 μm and the lands having a width of about 0. An ironing die less than 38 mm,
A can bodymaker punch with additional roughness, having a Ra of greater than 0.35 μm and an isotropic texture,
To at least one of the peculiarities of

To this end, the manufacturing method contacts as material the outer surface, which has a roughness Ra of typically less than 0.3 μm, in contact with the die, and the punch, which has a roughness Ra of typically more than 0.4 μm. Aluminum alloy sheet with internal surface and/or punch with additional roughness and isotropic texture characterized by Ra greater than 0.35 μm and/or infeed surface, which is advantageously a working area ( 7) and the land (8) with a radius of 0.5-4.6 mm rounded intersection (5), between the land and the exit surface (9) with a radius less than 1.2 mm. An ironing die with an intersection (6), a roughness Ra within the working area of less than 0.03 μm (see FIG. 4) and a short land width of typically less than 0.38 mm is used.

The present invention also provides the production of aluminum alloy beverage cans by "squeezing and ironing", characterized in that they use smooth-faced aluminum sheets on both sides in combination with a punch of additional roughness as defined above. It also relates to the method.

Advantageously, the manufacturing method of the present invention does not use any internal copper lubrication.

The invention also provides that the reflectivity measured at 60° is greater than 73% immediately after the last ironing step, ie before any supplemental surface treatment and without any supplemental surface treatment. And a beverage can manufactured by the method as described above.

It should be pointed out that the value of 73% is the average value. For example, with respect to FIG. 5 or 8, each point on the graph is obtained per production run producing about 8,000 to 10,000 cans, for 3 cans and 10 measurements per can. Is the average value calculated for.

The present invention also relates to an ironing die for an aluminum alloy beverage can manufacturing method by "squeezing and ironing", in which 0.5-4.6 mm between the feeding surface (7) and the land (8). Rounded intersection (5) of radius, rounded intersection (6) of radius less than 1.2 mm between land and exit surface (9), working part having roughness Ra less than 0.03 μm. It also relates to an ironing die, characterized by a surface in the zone and a land width of less than 0.38 mm.

Finally, the invention also relates to a can body making machine for a method for producing aluminum alloy beverage cans by "squeezing and ironing", characterized in that they have a roughness Ra of more than 0.35 μm and an isotropic texture. Also related to punching.

1 represents a typical "beverage can" can body with a "bottom" (dome) (11), "middle wall" (12) and "top wall" (13). Ironing step with punches (21), dies (22), "undeformed zones" (23), "deformed zones" (24), "deformed zones" (25) and "wall tension zones" (26) Represents "Feeding angle" (1), "Land width" (2), "Land angle" (3), "Exit angle" (4), "Acute intersection between feeding surface and land" (51), "Ironing" according to the state of the art with "acute intersection between land angle and exit angle" (61), "feed surface" (7), "land surface" (8), "exit surface" (9) "Working surface of the die". "Feeding angle" (1), "Land width" (2), "Land angle" (3), "Exit angle" (4), "Round intersection between feeding surface and land" (5 ), "rounded intersection between exit surface and land" (6), "feed surface" (7), "land surface" (8), "exit surface" (9). The "working surface of the ironing die with a rounded intersection" is shown. The "reflectance measured at 60" as a function of "metal roughness" is expressed. Here, the low roughness is 0.23 μm and the high roughness is 0.49 μm. Diamond points are average values. The "tear ratio" in ppm as a function of the "third ironing ratio" expressed in %, black is for a punch roughness Ra of 0.20 μm and white is for a roughness of 0.47 μm. Degree Ra. The average thickness range (maximum minus minimum) in μm as a function of land width in mm, the left side is for the intermediate wall (12) (FIG. 1) and the right side is for the upper wall (13). ) (FIG. 1). The "reflectance measured at 60" as a function of the sharpness of the intersection between the inflow surface and the exit surface and the land. Here, 0 relates to a rounded intersection (5) with a radius of 0.5 to 4.6 mm and a rounded intersection (6) with a radius of less than 1.2 mm, and 1 refers to an acute angle. It is related to the intersection (see FIG. 4). Diamond points are average values.

The glossy appearance of the exterior wall after ironing is an important property for the quality of the visual appearance of the finished finished product. This property can be qualitatively assessed using the haze effect and image clarity.

One of the best measurements to quantitatively assess it is the specular reflectance at 60° to the normal of the flattened can wall. All reflectance measurements discussed herein were performed on can preforms after post-ironing and cleaning operations similar to those performed in can factory.

The roughness is measured according to the NF EN ISO 4287 standard. An isotropic texture is a texture whose roughness measurement is independent of the measurement direction. For roughness Ra greater than 0.35 μm and isotropic textures, the roughness Ra is greater than 0.35 μm in all measurement directions.

In order to solve the problem, the present invention aims to reduce the friction between the ironing die and the metal at the same time as increasing the friction between the punch and the metal. In this way, a friction between the bodymaker punch and the aluminum sheet is generated that is higher than the friction between the ironing die and the aluminum sheet.

For this purpose, the following solutions are effectively used individually or in combination.

The first embodiment consists of using a metal with a differentiated roughness, i.e. an aluminum alloy sheet. More precisely, it has an external smooth surface in contact with the die, characterized by Ra below 0.3 μm, and an internal rough surface in contact with the punch, characterized by Ra above 0.4 μm. means.

The main advantage of using a smooth metal exterior is that it improves the can brightness to at least 73% at 60° reflectance. On the other hand, providing the interior with rough metal contributes to increased friction with the punch and thus to lower tear rate.

For a given top wall thickness, the gauge reduction of the middle wall is constrained by the ironing ratio of the third die. By using metals of different roughness, specifically higher internal roughness, it is possible to increase the critical third ironing ratio to above 44% and consequently reduce the intermediate wall thickness. it can.

The second embodiment uses a punch with an isotropic texture and an additional roughness characterized by Ra greater than 0.35 μm as compared to current cross-hatching practices well known to those skilled in the art. Consists of doing. This makes it possible to significantly increase the internal friction and consequently reduce the tear rate or increase the ironing ratio to more than 44% at the same tear rate.

For a given top wall thickness, the gauge reduction of the intermediate wall is limited by the ironing ratio of the third die. By using a punch of additional roughness, the critical third ironing ratio can be increased to over 44%, resulting in a reduction in intermediate wall thickness.

-Preferably, the manufacturing method of the present invention is functioning without any internal copper lubrication. This makes it possible to increase the internal friction and consequently reduce the tear rate or increase the ironing ratio at the same tear rate.

For a given top wall thickness, the gauge reduction of the intermediate wall is constrained by the ironing ratio of the third die, which cannot exceed the so-called "critical ironing ratio". Above this upper limit, any ironing process cannot be carried out without any problems. In the absence of internal copper lubrication, the "critical ironing ratio" is increased, making it possible to industrially implement a third ironing ratio of over 44%. As a result, the intermediate wall thickness can be reduced.

The variant, which consists of using smooth face sheets on both sides, contributes exactly to increasing the tear rate by reducing the friction between the punch and the metal. Yet such negative consequences can be prevented by using a combination of additional roughness punches or the absence of internal copper lubrication.

A third embodiment is a rounded intersection (5) with a radius of 0.5-4.6 mm between the feeding surface (7) which is the working area and the land (8), the land and the exit surface ( With rounded intersections (6) with radius less than 1.2 mm between 9), roughness Ra less than 0.03 μm in working area (see FIG. 4) and short land width less than 0.38 mm. It consists of using an ironing die.

This typically allows halving the current variability to allow better control of the top wall thickness, which improves the lightness of the can wall, ie 60° reflectance over 73%. Contribute to.

The efficiency of the necking line is sensitive to the variability of the top wall thickness, with higher variability triggering lower efficiencies. Rounded ironing dies with Ra less than 0.03 μm and/or shorter land widths typically less than 0.38 mm in the working area improve top wall consistency and thus necking line efficiency. Allows you to improve.

A rounded ironing die with Ra less than 0.03 μm and/or land width typically less than 0.38 mm in the working area improves top wall consistency and thus similar lower specification limits. Makes it possible to reduce the target of the top wall thickness.

Some examples of the above-mentioned correlation between metal, tooling and manufacturing parameters on the one hand, and manufacturability and glossy appearance of cans on the other hand, can be seen on the prototype drawing and ironing front-end line. Obtained during multiple test studies using a sheet of 3104 type alloy in H19 metallurgical temper with a 26 mm gauge. For each production run using a defined set of conditions, around 10,000 cans are produced and the occurrence of tears is counted. Can preform thickness, weight and reflectance are measured on samples taken from the beginning, middle and end of a production run.

The first example is taken from the same parent coil but with two different surface finishes, one with low roughness (Ra of 0.23 μm) and one with high roughness (Ra of 0.49 μm). Compare multiple production runs performed with the accompanying metal. FIG. 5 compares the effect of this symmetrical, i.e. identical on both sides, metal roughness on the can wall reflectance after ironing. Lower roughness provides higher reflectivity on average. Each point in FIG. 5 is the average value per production run of about 10,000 cans calculated for 10 measurements per can with 3 cans.

-The second example compares multiple production runs carried out with two punches having the same textured surface finish but different roughness Ra of 0.20 μm and 0.47 μm respectively. .. FIG. 6 shows that increasing the roughness of the punch reduces the tear rate on average for multiple third ironing ratios. Each point in FIG. 6 is obtained by testing about 8,000 cans with the same first and second ironing ratios.

-The third example concerns the variability of the wall thickness of the can during one production run. FIG. 7 shows that land width affects the thickness of the middle and top walls. That is, the shortest is the land size, and the most important is the thickness distribution. Each point in FIG. 7 is the average of 4 measurements per can for about 30 samples taken from one production run of about 10,000 cans. All production runs compared were done with the same punch, but with different die designs.

The fourth example deals with the effect of die design on reflectance. FIG. 8 shows, on average for multiple production runs with the same punch, a rounded intersection (5) with a radius of 0.5-4.6 mm (FIG. 4) and a radius of less than 1.2 mm. It has been shown that dies with certain intersections (6) (Fig. 4) allow the production of cans with higher reflectivity. More specifically, the combination of a metal with a smooth outer surface (Ra less than 0.3 μm) and a die with rounded intersections gives the best reflection, about 4% better than the standard case. It is possible to achieve a rate value (>74%).

1 feed angle 2 land width 3 land angle 4 exit angle 5 rounded intersection between feed surface and land 51 sharp intersection 6 between feed surface and land rounded between exit surface and land Intersection 61 An acute intersection between the land angle and the exit angle 7 Feed surface 8 Land surface 9 Exit surface 11 Bottom 12 Intermediate wall 13 Upper wall 21 Punch 22 Die 23 Undeformed zone 24 Deformed zone 25 Deformed zone 26 Wall tension zone

Claims (13)

In the method for manufacturing an aluminum alloy beverage can by "drawing/ironing", the friction between the can body manufacturing machine punch and the aluminum sheet is higher than the friction between the ironing die and the aluminum sheet,
An aluminum alloy sheet having an inner surface with a higher roughness than the outer surface,
An ironing die with rounded intersections between the feed surface or outlet surface and the land, the surface Ra in the working area being less than 0.03 μm and the width of the land being about 0.38 mm An ironing die that is less than
A can body-making machine punch having a roughness Ra of greater than 0.35 μm and an isotropic texture,
Characterized in that it is produced by at least one special property of,
The aluminum alloy sheet has an outer surface in contact with the die having a Ra coefficient of less than 0.3 μm and an inner surface in contact with the punch having an Ra coefficient of more than 0.4 μm,
A manufacturing method, wherein the punch has a roughness Ra of more than 0.35 μm and an isotropic texture . Process according to claim 1, characterized in that no internal copper lubrication is used. Said ironing die comprises a rounded intersection (5) between the feeding surface (7) and the land (8) with a radius of 0.5-4.6 mm, and between the land and the exit surface (9). Process according to claim 1, characterized in that it has rounded intersections (6) with a radius of less than 1.2 mm between them. Process according to claim 1, characterized in that a smooth-surfaced aluminum sheet with a roughness Ra of less than 0.3 μm is used on both sides, without being combined with any internal copper lubrication. The manufacturing method according to claim 1, characterized in that an aluminum alloy sheet having an Ra surface of less than 0.3 μm and having an outer surface in contact with a die is used as a material, and no internal copper lubrication is used. As material, using an aluminum alloy sheet with an Ra coefficient of less than 0.3 μm with an outer surface in contact with the die, and between 0.5 and 4. between the feeding surface (7) and the land (8). Roughness in the working area with a rounded intersection (5) with a radius of 6 mm and a rounded intersection (6) with a radius of less than 1.2 mm between the land and the exit surface (9). The manufacturing method according to claim 1, wherein an ironing die having Ra of less than 0.03 μm and a land width of less than 0.38 mm is used. Process according to claim 1, characterized in that a punch with an isotropic texture is used, with a roughness characterized by a Ra above 0.35 μm, and without any internal copper lubrication. .. Using a punch with an isotropic texture, with an additional roughness characterized by Ra above 0.35 μm, and between 0.5 and 4 between the feeding surface (7) and the land (8). A rounded intersection (5) with a radius of 6 mm and a rounded intersection (6) with a radius of less than 1.2 mm between the land and the exit surface (9), The manufacturing method according to claim 1, wherein an ironing die having a degree Ra of less than 0.03 μm and a land width of less than 0.38 mm is used. Not using any internal copper lubrication, and rounded intersections (5) between the feed surface (7) and the lands (8) with a radius of 0.5-4.6 mm, and the land and exit surfaces ( An ironing with a rounded intersection (6) with a radius of less than 1.2 mm between 9), a roughness Ra in the working area of less than 0.03 μm and a land width of less than 0.38 mm. The manufacturing method according to claim 1, wherein a processing die is used. Using as the material an aluminum alloy sheet with an outer surface in contact with the die having a Ra coefficient of less than 0.3 μm and an inner surface in contact with the punch having an Ra coefficient of more than 0.4 μm, more than 0.35 μm Process according to claim 1, characterized in that a punch with isotropic texture is used, with no additional roughness characterized by Ra of, and without any internal copper lubrication. Using as the material an aluminum alloy sheet with an outer surface in contact with the die having a Ra coefficient of less than 0.3 μm and an inner surface in contact with the punch having an Ra coefficient of more than 0.4 μm, more than 0.35 μm Using a punch with an isotropic texture with a roughness characterized by a Ra of 0.5-4.6 mm between the feeding surface (7) and the land (8). With a rounded intersection (5) and a rounded intersection (6) between the land and the exit surface (9) with a radius of less than 1.2 mm, the roughness Ra in the working area is 0. The manufacturing method according to claim 1, wherein an ironing die having a land width of less than 03 μm and a land width of less than 0.38 mm is used. Using as the material an aluminum alloy sheet with an outer surface in contact with the die having a Ra coefficient of less than 0.3 μm and an inner surface in contact with the punch having an Ra coefficient of more than 0.4 μm, more than 0.35 μm Using a punch with an isotropic texture, with a roughness characterized by a Ra of 0, no internal copper lubrication, and between the infeed surface (7) and the land (8). Having a radiused rounded intersection (5) of 0.5-4.6 mm and a radius rounded intersection (6) of less than 1.2 mm between the land and the exit surface (9), The manufacturing method according to claim 1, wherein an ironing die having a roughness Ra of less than 0.03 µm and a land width of less than 0.38 mm in the working area is used. In an ironing die for a method of manufacturing an aluminum alloy beverage can by "squeezing and ironing", a roundness with a radius of 0.5 to 4.6 mm between the feeding surface (7) and the land (8). An intersection (5), a rounded intersection (6) with a radius of less than 1.2 mm between the land and the exit surface (9), a surface in the working area having a roughness Ra of less than 0.03 μm, And an ironing die having a land width of less than 0.38 mm.

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